The invention relates to an endless sling having a textile protective cover comprising a first textile tube, and a second textile tube within the first textile tube to form a double tube structure. The first tube and the second tube are connected together along two respective oppositely positioned longitudinal edges to form an inner sheath and an outer sheath. The sling has a load-carrying core within the second textile tube that includes a plurality of endless fiber strands.
Endless slings of the type according to the invention are defined quite generally in DIN [German Industrial Standard] 61360. Their basic structure and manner of fabrication are disclosed in DE-2,716,056.A1. There, normal tubular fabrics are employed for the protective tubes on such endless slings. From a weaving technology aspect, a tubular fabric is a woven band of two layers of fabric which lie on top of one another during weaving, with both their longitudinal edges being connected with one another by the manner in which the weft threads are guided or by a special manner of interlacing them.
For some time, a double-sheathed tube has also been used as the protective tube for such endless slings; in general use, this is called a double tube. Such a double tube is not composed of two boxed, completely separate tubes. Rather, with respect to weaving technology, it constitutes a woven band having four superposed layers of fabric that are produced in one weaving process and are connected with one another, from a textile technology aspect, at both their longitudinal edges basically in the same manner as described above by the manner in which the weft threads are guided or by a specific way of interlacing them. Thus the double tube is given an inner sheath and an outer sheath which, however, are limited to the regions between the two longitudinal edges extending in the longitudinal direction of the tube.
Compared to the conventional single protective tube, the double tube offers certain advantages, among them that of better flexibility and adaptability to the outer contours of the load to be hoisted. In this connection it is assumed that the individual wall thickness of the inner sheath and the outer sheath of the double tube of an endless sling is less in each case than the wall thickness of the single protective tube of an endless sling of the same size.
According to the technical guidelines for abutment means, an endless sling must be discarded as no longer usable if the protective tube is damaged to the extent that the load-carrying fiber strands can be seen through the protective tube, that is, are exposed. According to this definition, an endless sling equipped with a double tube is still usable if only its outer sheath is damaged, while the inner sheath is still intact in this damaged region, that is, the load-carrying fiber strands are completely encased, thus remaining invisible from the outside.
If there is easily visible damage to the outer sheath of an endless sling equipped with a double tube, it is difficult to unequivocally determine whether at least the inner sheath is indeed undamaged. This is particularly difficult if the easily visible damage to the outer sheath developed under load, that is, during use of the endless sling. Due to the stretchability and displaceability of particularly the inner sheath with respect to the outer sheath of such an endless sling, it easily happens under load that the inner sheath is displaced by a few centimeters relative to the outer sheath. If in such a case, not only the outer sheath is damaged but also the inner sheath at the same location, with the latter having been displaced out of its normal position relative to the outer sheath by the action of the load, this damage to the inner sheath can no longer be unequivocally determined or evaluated during the customary visual check in the unloaded state. In the unloaded state of the endless sling, the inner sheath and the outer sheath have been shifted back to their original, low-tension position relative to one another so that the damaged locations at the inner sheath and at the outer sheath are no longer congruent on top of one another but may be offset relative to one another by even several centimeters.